Cervico-medullary compression ratio: A novel radiological parameter correlating with clinical severity in Chiari type 1 malformation

Objectives: Chiari malformation type 1 (CM-1) is associated with cough headache, intracranial hypertension, cerebellar and spinal cord symptoms/signs. Herniated cerebellar tonsil length (HCTL) is widely used radiological parameter to determine the severity of CM-1, but with limited utility due to its weak correlation with some clinico-radiological findings. In this study, we aimed to evaluate a novel, practical parameter (cervico-medullary compression ratio; "CMCR") for its relationship with clinico-radiological findings in CM-1. Patients and methods: Thirty-five adult patients (17 F, 18 M) with CM-1 were included in this retrospective study. Head CT and craniospinal MR images were assessed. CMCR was calculated as the ratio of herniated cerebellar tonsil surface area to foramen magnum surface area, and HCTL was measured. These two parameters were correlated with clinical and radiological findings. Results: The mean CMCR was 0.60 +/- 0.15 and mean HCTL was 8.91 +/- 3.4 mm with no significant difference between gender and age groups for both parameters. For cough headache (0.64 +/- 0.14 vs 0.52 +/- 0.15, p = 0.043) and syringomyelia (0.67 +/- 0.11 vs 0.56 +/- 0.16, p = 0.039), only CMCR; for intracranial hypertension (CMCR: 0.64 +/- 0.14 vs 0.55 +/- 0.16, p = 0.049; HCTL: 9.66 +/- 3.59 mm vs 7.79 +/- 3.03 mm; p = 0.045) and cerebellar symptoms (CMCR: 0.65 +/- 0.14 vs 0.54 +/- 0.16, p = 0.048; HCTL: 10.4 +/- 3.5 mm vs 7.4 +/- 2.8 mm, p = 0.041), both CMCR and HTCL were significantly different between patients with and without respective findings. However, neither CMCR nor HTCL was different between patients with and without spinal cord symptoms and hydrocephalus. Conclusion: CMCR is a superior numerical parameter than HCTL for the assessment of clinical severity in CM-1 cases and needs further validation with larger studies.